Was the vinyl of the type you see in automotive interiors? Kinda spongy after forming? Can you post some pics of the stuff?

Sintra (a slighly-foamed rigid vinyl "sign foam") wouldn't be good in cars. Its thermoforming temperature is so low that it would be somewhat soft and weak in a hot car on a sunny day. (It's mostly used for interior signage.)

EVA foam may be used in cars; I'm not sure. It's a rubbery vinyl (Ethylene Vinyl Acetate) foam that's used for a whole lot of things, in different thicknesses and densities. (Camp mats, flip flops, athletic shoe soles, padding for sports gear, cushioned grips for tool handles, floor cushioning tiles for workshops and play areas, etc.)

It's easy to get for experiments because it's sold in 9 x 12 and 12 x 18 sheets as "craft foam," in lots of colors and three thicknesses---2, 3, and 6 mm. (Unfortunately, the 6mm only seems to come in 9 x 12 sheets.)

So far, I've only done limited experiments. I can do the 2 & 3 mm foams just fine with my little over-and-under, heating from one side. It's suprisingly easy, as long as you don't expect the stuff to sag.

I played with the 6mm some, but the smoke made me stop---to heat it from both sides, I was using my kitchen oven, and I don't want vinyl smoke residues in the food. I intend to build a double-sided vacuum former oven at some point, maybe soon, and then I'll play with it more.

These are the only pictures of foam stuff I have up and linkable---experiments using life casts as bucks.

This one shows a plaster face cast (where most of the "detail" is flaws in the cast), and a 3mm and a 6 mm foam sheet formed over it:

These was done before I set up the high-vac, so he detail isn't good, especially on the 6 mm (black) one, which didn't really suck down. That gave a kind of ugly-and-disturbing-but-kinda-cool hockey-mask effect, so we made some halloween masks out of them, and a photographer at a party took our picture:

(That's where my avatar picture came from.)

If you cook the 2 mm stuff long and slow, it cooks down to about 1 mm thick and gets sorta leathery rather than foamy, with a nice surface texture. (That may be a bad idea, and the plastic may deteriorate after being overcooked like that, but at least at first it's kinda cool.)

Here's one of those:

I have some more recent 3mm ones using the high vac, with better detail, but no pictures yet. I'm pretty sure the 6mm will suck down fine with high vac, too. With a good oven, I'm optimistic I can do 3/8" stuff and maybe 1/2".

Here's what happens when you cook craft foam a little too hot for a little too long---it just starts to disintegrate, without ever sagging:

They're selling conductive EVA in 37 x 57 inch sheets. (Why those dimensions? No idea.) The 1/8" foam is 18.50 and the 1/4" is $37.

I'm sure there are cheaper places to get the stuff, especially if you don't need conductive foam, but I haven't really looked.

I'm pretty sure I came across smaller sheets for sale for making prosthetics, but they weren't particularly cheap, either.

If I knew exactly what I wanted, I'd probably just call up our local foams distributor; they have or can get pretty much any kind of plastic or rubber foam, but I wouldn't be surprised if they have a $100 minimum order.

Here's one of the places that sells EVA foam sheets for prosthetics, in a variety of colors (including multicolor swirls) and awkward sheet sizes. Nice variety of thicknesses. No prices listed; you can request their catalog online.

Great stuff thanks!! You inspire me to build a more complex over under machine. Thanks for the link to the Starship modeler I have been helping him with some of his aerodynamic difficulties. I have asked why he changed course and went to balsa but haven't got a response yet. I thought the foam version was way cool. I think a balsa structure covered with a thin vacuum formed polystyrene shell might be the ticket. So many ideas so little time!

Rick_________________We the unwilling, led by the unqualified have been doing the impossible now with so little for so long we now feel we can do anything with nothing.

I just noticed that McMaster-Carr sells gray EVA foam in various thicknesses (including 1/8", 1/4", 3/8", & 1/2") in 47 x 29 inch sheets. The 1/4" is a little under $16 a sheet, and the 1/8" is about $8.50. They also have 12 x 12 inch sheets._________________Paul (a.k.a. Dr. Crash)

I just noticed the stuff at McMaster is textured both sides, so it's probably useless for most vacuum forming purposes. (But not all; if you're making a cushioned liner or other kind of inner layer, it might not matter.)_________________Paul (a.k.a. Dr. Crash)

That is very interesting, thanks for sharing your results! I had an idea for a Halloween costume, and I was even thinking of craft foam for a few of the parts, but it never occurred to me that it could be vac-formable. If nothing else, it seems to make a cool mask.

I'm not vacuum forming foam-backed vinyls, or other pre-laminated stuff; that sounds very tricky.

I probably shouldn't have said/thought that. Thinking about it more, I'm guessing that some of the laminates designed for thermoforming are pretty easy to vacuum form. (And if you know where to get them relatively cheaply in small quantities, let me know...)

That would probably be the way to go, for a lot of purposes---easier than hassling with laminating things yourself.

It's not "strong" at all in the sense of being rigid. It's still a rubbery foam.

It's also not very strong on the surface---it's easy to dent or scuff it. It's not like vinyl that you'd put on a chair seat, or make a real shoe out of.

I think for those kinds of purposes, there are easily-vacuum-formed vinyls out there, but I haven't done the research to figure out what to get and where to get it cheaply in small quantities.

For making more rigid structures, some people vacuum form extruded polystyrene foam, but it's tricky---at least if you use the very light stuff RC modelers usually use. You have to heat it very evenly, or you mess up hotter parts of it before the cooler parts get hot enough all the way through.

(Or it could be that none of those guys has built a good oven, and it's not really all that hard if your oven is even decent. Regular polystyrene is very forgiving, and it's not really clear to me why foamed polystyrene shouldn't be fairly forgiving, too, like EVA foam. But I may be missing something.)

I'm thinking that denser and thinner extruded polystyrene foam might be much easier to heat & form, because it would conduct heat better. If it was as easy to form as EVA, that would be great, so long as you didn't need the extreme lightness modelers sometimes want. (Even for flying models, I'd think you could usually use denser and thinner foam for the skin, if you have a few spars and ribs/bulkheads.)_________________Paul (a.k.a. Dr. Crash)

Thanks for posting the link for where we can purchase the EVA foam. It's nice to be able to get recommendations and tips from people who are experienced, since I am new to the business. I appreciate any helpful tips and hints!_________________I love candy!
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